Semiconductor devices are fabricated on silicon wafers. The silicon wafers may be sliced from a single-crystal silicon ingot. The single-crystal silicon ingot may be grown by using suitable crystal growth techniques. The crystal growth techniques may be divided into two categories, namely the Czochralski crystal growth method and the floating zone crystal growth method.
The Czochralski crystal growth method comprises separating metallurgical grade silicon (MGS) from silicon dioxide (SiO2) through the reaction between SiO2 and carbon (C), refining MGS to yield semiconductor grade silicon (SGS), heating the silicon to the melting point of silicon (1412 degrees), melting silicon to form liquid silicon in a Czochralski silicon puller, inserting a seed crystal into the liquid silicon, raising the seed crystal slowly from the liquid silicon so as to allow a single-crystal layer to grow on the seed crystal.
The Czochralski crystal growth process may include several stages such as a neck region growth stage, a shoulder region growth stage, a body growth stage and a tail region growth stage. At the end of the crystal growth process, a single-crystal ingot is pulled from the Czochralski silicon puller.
The floating zone crystal growth method comprises clamping a polycrystalline silicon rod with one end in contact with a single-crystal seed layer, placing a radio frequency (RF) heating coil surrounding a lower portion of the polycrystalline silicon rod, heating the lower portion of the polycrystalline silicon rod beyond the melting point of silicon through eddy currents induced by the RF heating coil, forming a melt zone between the single-crystal seed layer and the upper portion of the polycrystalline silicon rod, solidifying the melt zone on the single-crystal seed layer to form a single-crystal having the same crystalline direction as the single-crystal seed layer.
One advantage of having the floating zone crystal growth method is that the silicon growth process does not require a container. As a result, the floating zone crystal growth method helps to prevent contamination and improve the purity of the single-crystal ingot.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.